1. Field of the Invention
The invention generally relates to radio measurement collection for Minimization of Drive Tests (MDT), and more particularly, to apparatuses and methods for report availability of the MDT logs during inter-Radio Access Technology (RAT) handovers.
2. Description of the Related Art
In a typical mobile communication system, an operator needs to run manual drive-tests to adjust network settings for performance optimizations, including radio coverage optimization, mobility optimization, network capability optimization, channel optimization, Quality of Service (QoS) verification, network planning, and others. In order to reduce the cost and time consumed for the manual drive-tests, a Minimization of Drive Tests (MDT) concept has been proposed, which requires the user equipment (UE) to log its measurement results and report the measurement logs (referred to herein as MDT logs) to the service network, so that the operator may analyze the MDT logs and adjust the network settings without too much burden of the manual drive-tests.
Taking the Long Term Evolution (LTE) technology in compliance with the 3GPP TS 37.320 specification, v1.0.0 (referred to herein as the 37.320 specification), and the 3GPP TS 36.331 specification, v1.0.0 (referred to herein as the 36.331 specification) as an example, after a UE is powered on and connected to a UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network (UTRAN) or evolved-UTRAN (E-UTRAN), the UTRAN or E-UTRAN may initiate an MDT measurement configuration procedure with the UE by transmitting an IdleMDTConfiguration message, to indicate the configuration parameters for logged MDT measurements in an idle mode, as shown in FIG. 1. When the UE enters the idle mode from a connected mode, it performs measurement logging according to the configuration parameters in the IdleMDTConfiguration message. Later, when the UE is paged or the user of the UE wishes to make a call, it initiates a Radio Resource Control (RRC) connection establishment procedure by transmitting an RRCConnectionRequest message to the UTRAN or E-UTRAN. Upon receiving the RRCConnectionRequest message, the UTRAN or E-UTRAN replies to the UE with an RRCConnectionSetup message. According to the configuration parameters included in the RRCConnectionSetup message, the UE establishes the RRC connection with the UTRAN or E-UTRAN and further transmits an RRCConnectionSetupComplete message to the UTRAN or E-UTRAN upon completion of the RRC connection establishment. Particularly, the UE includes the information concerning the availability of the MDT logs in the RRCConnectionSetupComplete message. As shown in FIG. 2, if the availability of the MDT logs is indicated, the UTRAN or E-UTRAN may request the UE to report on the MDT logs, by transmitting a UEInformaqtionRequest message to the UE. When receiving the UEInformaqtionRequest message, the UE replies to the UTRAN or E-UTRAN with a UEInformaqtionResponse message which includes the measurement logs.
However, there are situations where the UE can not indicate the availability of the MDT logs to the UTRAN or E-UTRAN, causing the UTRAN or E-UTRAN unable to retrieve the MDT logs. Taking an inter-RAT (Radio Access Technology) handover procedure from a UMTS system to an LTE system as an example, the UE is initially camped on the LTE system and configured to perform MDT measurement logging for the LTE system. Upon moving to an area with stronger signal coverage of the UMTS system, the UE stops the MDT measurement logging and reselects to the UMTS system. Later, in response to a request for a Mobile Originated (MO) call or a Mobile Terminating (MT) call, dedicated radio link(s) is established for the UE to the UMTS system. During the MO call or MT call, the UE is handed over to the LTE system from the UMTS system if the UE is moved back to the area with the stronger signal coverage of the LTE system. It is noted that, although MDT logs for the LTE system are available from the MDT measurement logging performed before reselection to the UMTS system, the UE does not report to the LTE system about the information concerning the availability of the MDT logs when being handed over back to the LTE system. As a result, the LTE system is not able to retrieve the MDT logs from the UE. Similarly, in another example of an inter-RAT handover procedure from an LTE system to a UMTS system, if the MDT logs for the UMTS system are available from a previously performed MDT measurement logging and the UE is handed over back to the UMTS system from the LTE system during an ongoing MO call or MT call, the UE does not report to the UMTS system about the information concerning the availability of the MDT logs. Thus, it is desirable to have an efficient way of reporting the availability of the MDT logs to the service network.